DESCRIPTION: The applicants propose to investigate how the density of two naturally processed HIV peptides(ILKEPVHGV,IV9< from HIV reverse transcriptase and SLLYNTVATL, SL9 from HIV-1 gag) on target cells affects the induction of early(cytolysis) and late (proliferation and lymphokine production) responses of human CD8 CTL clones that recognize these peptide class I MHC. Comparison between the peptide's natural abundance(number of peptide molecules that can biochemically isolated from the infected cells) and the number of ppepMHC complexes on the target cells required to induce T cell response will provide a unique opportunity to determine whether the limited number of naturally processed HIV-derived peptides is sufficient to trigger proliferation and lymphokine production by HIV-specific CTL. In addition they will measure equilibrium and kinetic constants for the binding of cognate soluble pepMHC complexes to the T-cell receptor(TCR) on live CTL and will determine how strength(affinity) and stability(life-time) of TRC-pepMHC binding correlates with efficiency of various HIV-specific T cell responses. They will also compare responsiveness of various CD8 CTL from different HIV-infected individuals that all recognize the same immunodominant HIV-derived peptide SL9 and will determine how affinity and kinetics of TCR-pepMHC binding affect the CTL response to the immunodominant HIV peptide epitope Finally, they will investigate whether SL9-specific CTL clones whose TCR bind stronger to cognate pepMHC complex are more effective in suppressing viral replication in HIV-infected cells in vitro. The results of these studies are expected to aid efforts to develop vaccines or immunotherapeutic agents to elicit virus-specific CTL activity.